Cancer is a disease that is the number one cause of death in developed countries, which is caused by mutations in various cancer genes and cancer-suppressing genes in normal cells. The mutations in cancer genes and cancer-suppressing genes mostly result in the activation of the proliferation signaling and a failure in the apoptosis-regulating signals (inhibition of apoptosis). Further, cancer includes localized types, which are cancers that are limited to the primary lesions, and distant metastatic types, which are cancers that metastasize to other organs. Distant metastatic cancers have much lower 5-year-survival rates than localized cancers.
For example, breast cancer is by far the most common cancer in women worldwide and still ranks second in cancer mortality rates by site in developed countries. Breast cancer is associated with a variety of lifestyle choice, such as obesity, later onset of first childbirth, and the use of hormone replacement therapy (Non-patent Document 1). Breast cancer bone metastasis occurs in 70 to 80% of patients with advanced breast cancer, leading to severe pathological bone fractures, pain, hypercalcemia, and spinal cord and nerve-compression syndromes, which are the primary causes of morbidity and mortality.
Cancer therapies include surgery, radiotherapy, and drug therapy. As described above, because bone metastasis, etc. are highly likely to occur in patients with advanced breast cancer, they are usually treated not only with locoregional therapies such as surgery and radiotherapy, but also with combined systemic therapy such as drug therapy. At this point, drug therapy for breast cancer includes chemotherapy using anticancer drugs, hormonal therapy involving administering antiestrogen agents, etc. for suppressing the action of estrogen, which accelerates the proliferation of breast cancer, and molecularly targeted therapy using drugs that target and attack molecules unique to cancer cells (for example, HER2 protein in breast cancer). Also, means for preventing cancer include improvement in lifestyle habits such as smoking cessation and improvement in diet. Recently, chemoprevention, which involves administering drugs, supplements, vaccines, or other agents to reduce the risk of infection and delay the progression of breast cancer, has been proposed (Non-patent Document 1).
The present inventors have conducted research of various edible marine algae such as Undaria pinnatifida, Eisenia bicyclis, Gelidium amansii, and Ulva pertusa Kjellman, and proposed a bone mass-increasing composition exerting an antiosteoporotic action comprising, as an active ingredient, a processed product of Sargassum horneri, which is known to be marine algae of the genus Sargassum in the order Fucales, the prolific brown algae inhabiting shallow seas (Patent Document 1), an agent for preventing or improving diabetic conditions comprising Sargassum horneri or a processed product thereof as an active ingredient (Patent Document 2), an NF-κβ inhibitor comprising Sargassum horneri or a processed product thereof as an active ingredient (Patent Document 3), and a method for suppressing differentiation of bone marrow mesenchymal stem cells into adipocytes using Sargassum horneri or a processed product thereof (Patent Document 4). However, the effects of Sargassum horneri or a processed product thereof on cancer cells have not been known to date.